The invention relates to a process for the catalytic hydrogenation of a heavy hydrocarbon oil at elevated pressure and temperature by passing said hydrocarbon oil through a number of reactors which are arranged in series and contain substantially fixed catalyst beds, in which process the deactivated catalyst present in the reactors is continuously or periodically replaced by fresh catalyst.
For the hydroconversion (particularly demetallization and/or desulphurization) of heavy and particularly residual, hydrocarbon oils in the presence of hydrogen with a catalyst, use can be made of a system of a number of reactors, which contain substantially fixed catalyst beds and can be arranged in series, the stream of hydrocarbon oil being conducted through all the reactors consecutively.
By a substantially fixed catalyst bed is meant a catalyst bed which may contract or expand by less than 10% during the process, depending on whether process is carried out in downflow or upflow of the feed respectively. Said 10% contraction or expansion of the catalyst bed relates to the volume of the catalyst bed during the process in comparison with the volume occupied by the loosely packed catalyst bed in hydrocarbon oil with no oil flowing through the bed.
When use is made of catalysts which are present in reactors as a substantially fixed bed, the catalyst activity may decrease, for example by deposition of coke, tarry products and metals. In a number of cases reactivation, for example by burning off, is possible, but metals deposited on the catalyst cannot be removed in this manner. Moreover, burning off is often objectionable, since the hydrogen-containing gas present in the reactor must be removed therefrom substantially completely before oxygen-containing gas can be admitted. For these reasons it is usually attractive to remove the deactivated catalyst from the reactor and replace it by active catalyst. A number of processes are known and are described e.g., in U.S. Pat. Nos. 2,963,525, 3,547,809 and 4,017,382.
In order to enable the stream of hydrocarbon oil to be optionally passed or not passed through each reactor and the catalyst to be supplied to or removed from each reactor, each reactor is provided with means for the supply and removal of feed and catalyst, which are so designed that each reactor can be separately connected to and disconnected from the supply and removal lines of both feed and catalyst.
During operation the catalyst in a reactor can be replaced by continuously or periodically removing a quantity of deactivated catalyst from this reactor and (in general simultaneously or subsequently ) supplying about the same quantity of fresh catalyst to said reactor.
When the catalyst in a reactor has become deactivated to such an extent that its complete removal is required, it is also possible to disconnect this reactor from the supply and removal lines of the hydrocarbon mixture, remove the catalyst from the reactor and replace it by fresh catalyst.
The catalyst can be removed by dumping it by gravity into a high-pressure lock, i.e., enclosure, which has been brought to the same hydrogen pressure as the reactor.
After isolation of the reactor the lock can be brought to atmospheric pressure and the deactivated catalyst can be dumped into a storage tank which is situated at a lower level. The fresh catalyst can be supplied to the reactor from a high-pressure lock by dumping it by gravity. In order to prevent clogging the valves in the said provisions for catalyst supply and removal must have a large diameter, which makes them complicated and expensive to construct.
In order to ensure a good sealing when the valve is closed, solid catalyst remnants must be removed before closure. The catalyst remnants can be removed by passing an oil stream along the valve at high speed. In the case of large valves this requires a very large oil throughput, since the quantity of oil which must be passed through in order to obtain a given flow rate is proportional to the square of the valve diameter.
Moreover, arrangements in which the catalyst is supplied to or is removed from the reactor by gravity, in the case of the present very large reactors result in very tall and often unacceptably high plants, since both above and below the reactor a lock and a catalyst storage tank must be present.
It is also felt as a drawback that a large number of high-pressure locks is necessary, since each reactor must be provided with two high-pressure locks and storage tanks, including the above-mentioned appurtenant expensive and complicated large-diameter valves.
The invention provides a process in which the necessary number of high-pressure locks is much lower, the valves to be used therein may have a smaller diameter and the number of tanks into which the deactivated catalyst is passed and from which the fresh catalyst is supplied, is also much lower and these tanks, like the high-pressure locks, need not be situated below and above the reactors respectively.